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Centrifugal Compressor Performance Curves


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Posted 19 March 2019 - 05:57 AM

Hello everyone,


I am trying to evaluate the actual performance of the centrifugal compressor.

Vendor has provided performance curves at single speed (let us say- X RPM) only.

In actual, compressor is running at different speed (let us say - X / Y / Z etc).


How can we obtain new curves at running or operating speed.

I tried using affinity or fan laws, but that is not giving satisfactory results at much higher speed than the speed (X RPM) given by vendor. At near about similar RPM (X RPM), results are matching with performance curves.


How to tackle such situation.



#2 thorium90


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Posted 19 March 2019 - 06:42 AM

I would think, ask the vendor to give you the curves for the lower speeds?

Say 80%, 60%, 45%...


I think it doesn't match with affinity law because you have a constant head application, or at least a certain head to overcome in the discharge line... Common mistake to simply reduce the speed with affinity law and thinking the flow will drop accordingly, but many forget that reducing speed also reduces pressure and therefore, to maintain the same pressure you have to speed up again to maintain the required flow and pressure. So then they get confused why the affinity laws don't apply. It does, but when its an open discharge to atmosphere or something similar where there is no head required.

Edited by thorium90, 19 March 2019 - 09:27 AM.

#3 oilpmp


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Posted 06 June 2019 - 08:49 AM

You need to use fan laws as first approximation, but as you pointed out, as you will move further away from the reference speed (for which data ara available from OEM), the fan laws will produce results which may be too innacurate.


Otherwise, you probably need to look for a professional package such as n-centrix for compressor field performance or equivalent. These tools can be very accurate, but you need to have each of your reference curve from vendor provided on a range of mach numbers (even though the speed is given as single value). Just to recall the concept, Mach number (the peripheral one) is function of  gas composition,  inlet temperature, pressure and combination thereof. I suppose, you could check based on the vendor information you have at hand.

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